A PWM signal generation unit generates a PWM signal based on a driving voltage so that a midpoint of the longer period out of an H level period and an L level period in each PWM period matches a midpoint of the PWM period. FETs of a full bridge circuit (a driving circuit) are driven according to a PWM signal, and a driving current that corresponds to an A-phase is supplied to a stepping motor. A current detector detects a driving current flowing through an A-phase winding of the motor based on a voltage that is generated across a shunt resistor, at a fixed time point that is in each PWM period and in the H level or L level period that is at the center of the PWM period.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A motor control apparatus comprising: a driving circuit that includes a plurality of switching elements constituting an H bridge circuit, and to which a winding of a motor is connected; a detector configured to detect a driving current flowing through the winding; a voltage generator configured to generate a driving voltage for the driving circuit based on the driving current detected by the detector; and a pulse generator configured to generate a first PWM (Pulse-Width Modulation) signal and a second PWM signal that control ON and OFF operations of the plurality of switching elements, the first PWM signal being generated based on both the driving voltage generated by the voltage generator and a first triangle wave that serves as a carrier wave, and including a pulse at a first level that is one of a high level and a low level, and a pulse at a second level that is the other one of the high level and the low level, and the second PWM signal being generated based on both the driving voltage generated by the voltage generator and a second triangle wave that is in antiphase with the first triangle wave, and including a pulse at the first level and a pulse at the second level; wherein a driving voltage in a first period is smaller than a predetermined value and a driving voltage in a second period is greater than or equal to the predetermined value, the first period being a period in which the first PWM signal generated by the pulse generator is at the second level and including a timing when the detector detects the driving current, the second period being a period in which the second PWM signal generated by the pulse generator is at the first level and including a timing when the detector detects the driving current.
2. The motor control apparatus according to claim 1 , wherein the voltage generator is configured to generate the driving voltage such that a deviation between a driving current that is detected by the detector and a driving current that is to be supplied to the winding decreases.
3. The motor control apparatus according to claim 2 , wherein the pulse generator includes: a carrier generator configured to generate the first triangle wave; a reverser configured to generate the second triangle wave by reversing a phase of the first triangle wave according to a polarity, which is positive or negative, of the driving voltage that is generated by the voltage generator; and a comparator configured to, if the driving voltage is greater than or equal to 0, generate the second PWM signal by comparing the driving voltage with the second triangle wave, and if the driving voltage is negative, generate the first PWM signal by comparing the driving voltage with the first triangle wave.
4. The motor control apparatus according to claim 1 , wherein the detector is configured to detect the driving current in each cycle of the first triangle wave.
5. The motor control apparatus according to claim 1 , wherein the detector is configured to: when the detector detects the driving current in the first period, detect the driving current at a time point when the first triangle wave first takes an extremum after the first PWM signal has switched from the first level to the second level; and when the detector detects the driving current in the second period, detect the driving current at a time point when the first triangle wave first takes an extremum after the second PWM signal has switched from the second level to the first level.
6. The motor control apparatus according to claim 1 , wherein the plurality of switching elements are ON if the first PWM signal is at the first level, the plurality of switching elements are OFF if the first PWM signal is at the second level, the plurality of switching elements are ON if the second PWM signal is at the first level, the plurality of switching elements are OFF if the second PWM signal is at the second level, and the detector is configured to not reverse the polarity of the driving current when the detector detects the driving current in a period in which the first PWM signal is at the first level or a period in which the second PWM signal is at the first level, and reverse the polarity of the driving current when the detector detects the driving current in a period in which the first PWM signal is at the second level or a period in which the second PWM signal is at the second level.
7. The motor control apparatus according to claim 1 , wherein the pulse generator, the driving circuit, and the detector are provided for each of a first phase of the motor and a second phase of the motor, a triangle wave that corresponds to the first phase is synchronized with a triangle wave that corresponds to the second phase, the detector that corresponds to the first phase is configured to detect a driving current flowing through a winding that corresponds to the first phase, the detector that corresponds to the second phase is configured to detect a driving current flowing through a winding that corresponds to the second phase, the motor control apparatus further comprises a phase determiner configured to determine a rotational phase of a rotor of the motor based on: the driving current flowing through the winding that corresponds to the first phase, and that is detected by the detector that corresponds to the first phase; and the driving current flowing through the winding that corresponds to the second phase, and that is detected by the detector that corresponds to the second phase, and the motor control apparatus is configured to control the motor by controlling the driving current flowing through the winding that corresponds to the first phase and the driving current flowing through the winding that corresponds to the second phase, such that a deviation between an instruction phase that indicates a target phase of the rotor of the motor and the rotational phase that is determined by the phase determiner decreases.
8. The motor control apparatus according to claim 7 , further comprising: a voltage determiner configured to determine a value of an induced voltage that is induced in the winding that corresponds to the first phase and a value of an induced voltage that is induced in the winding that corresponds to the second phase, based on the driving currents that are detected by the detectors, the induced voltages being induced by a rotation of the rotor of the motor, wherein the phase determiner is configured to determine the rotational phase based on the value of the induced voltage corresponding to the first phase and the value of the induced voltage corresponding to the second phase that are determined by the voltage determiner.
9. The motor control apparatus according to claim 8 , wherein the motor control apparatus is configured to control the motor based on a torque current component that is a current component of a current value represented in a rotating coordinate system with the rotational phase as a reference, such that the deviation between the instruction phase and the rotational phase that is determined by the phase determiner decreases, the torque current component being a current component that generates torque in the rotor.
10. The motor control apparatus according to claim 1 , wherein the predetermined value is a value of 0.
11. The motor control apparatus according to claim 1 , wherein the driving circuit is a circuit in which, one end of a first switching element and one end of a second switching element are connected to a power supply, one end of a third switching element is connected in series to the other end of the first switching element, one end of a fourth switching element is connected in series to the other end of the second switching element, a resistor is connected to the other end of the third switching element and the other end of the fourth switching element, the resistor is grounded, and one end of a winding of the motor is connected to a conducting line that connects the first switching element and the third switching element to each other, and the other end of the winding of the motor is connected to a conducting line that connects the second switching element and the fourth switching element to each other.
12. The motor control apparatus according to claim 11 , wherein PWM signals that are generated by the pulse generators are supplied to the first switching elements and the fourth switching elements of the driving circuits, and PWM signals that are respectively in antiphase with the PWM signals that are generated by the pulse generators are supplied to the second switching elements and the third switching elements of the driving circuits.
13. A sheet conveyance apparatus comprising: a conveyance roller configured to convey a sheet; a motor configured to drive the conveyance roller; a driving circuit that includes a plurality of switching elements constituting an H bridge circuit, and to which a winding of a motor is connected; a detector configured to detect a driving current flowing through the winding; a voltage generator configured to generate a driving voltage for driving the driving circuit based on the driving current detected by the detector; and a pulse generator configured to generate a first PWM (Pulse-Width Modulation) signal and a second PWM signal that control ON and OFF operations of the plurality of switching elements, the first PWM signal being generated based on both the driving voltage generated by the voltage generator and a first triangle wave that serves as a carrier wave, and including a pulse at a first level that is one of a high level and a low level, and a pulse at a second level that is the other one of the high level and the low level, and the second PWM signal being generated based on both the driving voltage generated by the voltage generator and a second triangle wave that is in antiphase with the first triangle wave, and including a pulse at the first level and a pulse at the second level, wherein a driving voltage in a first period is smaller than a predetermined value, and a driving voltage in a second period is greater than or equal to the predetermined value, the first period being a period in which the first PWM signal generated by the pulse generator is at the second level and including a timing when the detector detects the driving current, the second period being a period in which the second PWM signal generated by the pulse generator is at the first level and including a timing when the detector detects the driving current.
14. A document feeding apparatus comprising: a document tray on which a document is to be stacked; a conveyance roller configured to convey the document that is stacked on the document tray; a motor configured to drive the conveyance roller; a driving circuit that includes a plurality of switching elements constituting an H bridge circuit, and to which a winding of a motor is connected; a detector configured to detect a driving current flowing through the winding; a voltage generator configured to generate a driving voltage for driving the driving circuit based on the driving current detected by the detector; and a pulse generator configured to generate a first PWM (Pulse-Width Modulation) signal and a second PWM signal that control ON and OFF operations of the plurality of switching elements, the first PWM signal being generated based on both the driving voltage generated by the voltage generator and a first triangle wave that serves as a carrier wave, and including a pulse at a first level that is one of a high level and a low level, and a pulse at a second level that is the other one of the high level and the low level, and the second PWM signal being generated based on both the driving voltage generated by the voltage generator and a second triangle wave that is in antiphase with the first triangle wave, and including a pulse at the first level and a pulse at the second level, wherein a driving voltage in a first period is smaller than a predetermined value, and a driving voltage in a second period is greater than or equal to the predetermined value, the first period being a period in which the first PWM signal generated by the pulse generator is at the second level and including a timing when the detector detects the driving current, the second period being a period in which the second PWM signal generated by the pulse generator is at the first level and including a timing when the detector detects the driving current.
15. A document reading apparatus comprising: a document tray on which a document is to be stacked; a conveyance roller configured to convey the document that is stacked on the document tray; a reading unit configured to read the document that is conveyed by the conveyance roller; a motor configured to drive the conveyance roller; a driving circuit that includes a plurality of switching elements constituting an H bridge circuit, and to which a winding of a motor is connected; a detector configured to detect a driving current flowing through the winding; a voltage generator configured to generate a driving voltage for driving the driving circuit based on the driving current detected by the detector; and a pulse generator configured to generate a first PWM (Pulse-Width Modulation) signal and a second PWM signal that control ON and OFF operations of the plurality of switching elements, the first PWM signal being generated based on both the driving voltage generated by the voltage generator and a first triangle wave that serves as a carrier wave, and including a pulse at a first level that is one of a high level and a low level, and a pulse at a second level that is the other one of the high level and the low level, and the second PWM signal being generated based on both the driving voltage generated by the voltage generator and a second triangle wave that is in antiphase with the first triangle wave, and including a pulse at the first level and a pulse at the second level, wherein a driving voltage in a first period is smaller than a predetermined value a driving voltage in a second period is greater than or equal to the predetermined value, the first period being a period in which the first PWM signal generated by the pulse generator is at the second level and including a timing when the detector detects the driving current, the second period being a period in which the second PWM signal generated by the pulse generator is at the first level and including a timing when the detector detects the driving current.
16. An image forming apparatus, comprising: an image forming unit configured to form an image on a recording medium; a motor configured to drive a load; a driving circuit that includes a plurality of switching elements constituting an H bridge circuit, and to which a winding of a motor is connected; a detector configured to detect a driving current flowing through the winding; a voltage generator configured to generate a driving voltage for driving the driving circuit based on the driving current detected by the detector; and a pulse generator configured to generate a first PWM (Pulse-Width Modulation) signal and a second PWM signal that control ON and OFF operations of the plurality of switching elements, the first PWM signal being generated based on both the driving voltage generated by the voltage generator and a first triangle wave that serves as a carrier wave, and including a pulse at a first level that is one of a high level and a low level, and a pulse at a second level that is the other one of the high level and the low level, and the second PWM signal being generated based on both the driving voltage generated by the voltage generator and a second triangle wave that is in antiphase with the first triangle wave, and including a pulse at the first level and a pulse at the second level, wherein a driving voltage in a first period is smaller than a predetermined value and a driving voltage in a second period is greater than or equal to the predetermined value, the first period being a period in which the first PWM signal generated by the pulse generator is at the second level and including a timing when the detector detects the driving current, the second period being a period in which the second PWM signal generated by the pulse generator is at the first level and including a timing when the detector detects the driving current.
17. The image forming apparatus according to claim 16 , wherein the load is a conveyance roller that is configured to convey the recording medium.
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April 5, 2017
May 28, 2019
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